1. Field of the Invention
The present invention relates to an ophthalmologic apparatus.
2. Related Background Art
In the ophthalmologic medical field, fluorescent contrast photography or image pickup is widely conducted in which a fluorescent contrast medium is injected through a vein of a subject into an anterior or retinas and choroids. The fluorescent contrast medium injected into the vein of the subject reaches a subject eye via blood circulation. At first, the fluorescent contrast medium is gradually concentrated in the subject eye as time passes. After reaching a maximum level, the concentration of the fluorescent medium in the subject eye gradually decreases due to absorption and excretion by circulation in the body. That is, in fluorescent contrast photography, in principle, a photograph site becomes rapidly bright from a dark state, and then gradually darkens, as time passes after injection of the fluorescent medium.
In fluorescent contrast photography, the variations in brightness described above are important information for understanding the states of circulation of the body fluid in the eye and the body. Accordingly, the illuminating light intensity and the exposure conditions and sensitivity of photographing means-are not usually changed at the time of fluorescent contrast photography.
A silver halid film is mainly used as photographing means, but in recent years, electronic image photography using a CCD or the like has been performed (Japanese Patent Application Laid-Open No. H10-260487).
In the example of the conventional technique described above, however, the brightness of the subject changes rapidly with time. Photography using a conventional silver halid film has a wide latitude (exposure allowable range), thus making it possible to photograph an image having no problems in practice with respect to a change in brightness when the subject is being photographed.
However, electronic image pickup means has a latitude smaller than that of the silver halid film, so that the photographed image may be too dark with respect to a change in brightness of the subject, or the brightness may be saturated. Thus, for obtaining an appropriate image, a gain (signal amplification factor) or the illuminating light intensity must be changed but consequently, important information, i.e., a change in brightness of the subject described above, is lost, and the image thus obtained is very difficult to use for diagnosis for circulation.